const button = document.querySelector('.box>button')
const ul = document.querySelector('.box>.input-box')
button.onclick = () => {
  let firstELement = ul.firstElementChild
  if (!firstELement) {
    let li = `<li><input type="text" placeholder="输入关键字" value='1'/></li>`
    ul.innerHTML = li
  } else {
    let li = firstELement.cloneNode(true)
    ul.appendChild(li)
  }
}
